Radiance Measurement on Ramp Loading -- Implications for Temperature on Quasi-Isentropes

Temperature increases along a quasi-isentropic loading path have the promise to characterize either the approach to constant entropy in the case of a known Gr\"{u}neisen parameter or else to measure the Gr\"{u}neisen parameter once the quality of the isentrope is established. Our group has developed the ability to synthesize graded density impactors able to generate customized multistep loading paths that included ramp loads, dwells, shock jumps and ramp unloads. Here we present a recent measurement of thermal radiance from a ramp-loaded Sn sample. The sample was shocked to approximately 0.5 Mbar, held at a constant pressure for 400 ns, and then ramp loaded to approximately 1.5 Mbar. Dynamic emissivity was not measured along this path, but radiance was monitored at the sample-LiF window interface as a function of time at 7 wavelengths in the visible spectrum with a spectral resolution of 80 nm. We will discuss experimental results and analysis of the relationship between pressure and radiance on the ramp-loading path of Sn with variable initial temperature along the sample. Assumptions employed in this analysis and implications for temperature along the ramp-loading path, for the closeness of approach to isentropic loading, and for the Gr\"{u}neisen parameter of Sn will also be discussed.